Method of making straw paper



Patented Dec. 17, 1929 UNITED STATES PATENT OFFICE EDWARD B. WESTON, OF DAYTON, OHIO, AND WILLIAM G. CLARK, OF TERRE HAUTE, INDIANA, ASSIGNORS TO THE WESTON PAPER AND MANUFACTURING COMPANY, OF

DAYTON, OHIO, A CORPORATION OF OHIO No Drawing.

This invention is an improvement in methods of making straw paper, and in the paper, and more particularly in a method designed to produce a straw board especially ada )ted for corrugation, for use as the intermediate layer in composite boards for packing purposes.

Paper of the character in question should be of relatively light weight, and while possessing sufiicient strength to withstand crushing stress, must yet be flexible enough to enable corrugation without breaking. Straw board made by ordinary methods. it of sufiicient strength to resist crushing stress, and with sufi'i ient flexibility to enable corrugation without breaking, is diflicult to produce. W'hen of sufficient strength, it does not well adapt itself to corrugation, and if of flexibility sufficient to enable corrugation without breaking, it is not suiliciently resistant to err J'hing stress.

Caustic cooked straw produces a fiber which in paper making is known as a slow sheet. That is, the fiber so produced does not run fast eno gh over the paper machine. Lime cooked straw produces a fiber which runs fast over the paper machine, but the liber is relatively coarse and the product is relatively brittle. The caustic cooked straw PFOdlICt-S a. relatively fine fiber more easilydrawn out, and therefore makes a tougher sheet, but it is objectionable on account of the slowness with which it may be freed from water.

While caustic cooked straw makes a relatively hard and relatively stifi" sheet, the resu tant product is expensive; first, because of the cost of the chemicals used, and secondly, because of the slow speed of the paper machine. Hence, it is impossible to attain the normal tonnage of the machine.

One of the primary objects of the present invention is the provision of a. pulp containing long and fine fibers. but interspersedwith short coarse fibers, whereby a free stock is provided, that is, a stock from which the water may be easily removed by suction and pressure.

Another object is the provision of a method of preparing straw board, suitable for the Application filed February 15, 1929.

Serial No. 340,326.

purpose in view, in that the paper is tough to resist crushing and bending stresses, and capable of being produced at the rated speed of the paper machine. v

Another object is to produce a pulp, easily freed from water in the usual manner, and with suflicient long fiber to produce a. l ugh and flexible sheet.

Another object is the production of a paper especially fitted for the purpose in view.

In the present method, the pulp from which the paper is made is composed of about equal parts of caustic cooked straw and lime cooked straw, retained separately until thoroughly cooked and then mixed, whereby to provide a pulp which will give up its Water readily, and enable the machine to be oper ated at its rated capacity.

In carrying out the process, substantially equal quantities of straw are taken, as for instance, two batches of 7 tons each, and each batch is placed in a rotary. To one of the rotaries is added approximately 33,000 lbs. of water, and 1,100 lbs. of high calcium lime, the lime being slac-kcd in the water before it is pumped into the rotarv. In the other rotary is placed the same quantity of straw and water, Wi .h 500 lbs. of 78 caustic soda. Each batch is cooked for about seven hours, under 2? lb. steam pressure. The steam is then shut off, and the rotaries rolled in the steam for another two hours, before the excess steam is blown off.

The contents of the two rotarics are then emptied into the carriers at the same time, and the stock is carried to the stock pit and deposited in a single pile. In this way the two batches are thoroughly mixed, and from the mixture the heaters are furnished, and the stock is tl; 'oughly washed. The heater rolls are then put upon the pulp to draw it out. and prepare it for the paper machine. After beating the pulp goes through the Jordans and to the paper machines in the regular way. For the beating and washing, about two and one-half hours is required per beater.

Pulp prepared in this manner has sufiicient long fiber to enable substantially perfect corrugation, without any breaking, while at the same time it is relatively light in weight, tough and resistantto bending and crushing stresses. Pulp so produced provides a free fiber, which will run fast over the paper machine, allowing it to operate at the rated speed. The slow fiber of the caustic cooked straw, is freed by the fiber of the lime cooked straw, so that a fair average speed may be maintained in the machines. 4

While the cooking of straw with caustic soda and lime is known, wherein the lime and the soda are used in the same rotary, we are the first, so far as we are aware, to cook sepalate batches with caustic and lime, respectively, and retain them separate until after the cooking operation. When the lime and soda are used in the same rotary, the fiber will be of a homogenous nature, that is, all alike, and there will not be sufficient free stock to maintain high speed in the paper machine.

The proportions given above of lime and caustic soda cooked fiber, namely; a half and half mixture has proven' satisfactory, but this proportion ma be varied within fairly wide limits, depending upon the quality of paper sou ht, and the nature of the pulp produced. T e amount of lime per rotary can also be varied with satisfactory results, and the amount of caustic soda to some extent. The proportions given have proven satisfactory in practice. Experience has demon- Strated that paper produced by the improved process can be run at a higher speed over the corrugator than can straight caustic cooked straw, because the paper is of a stronger and more flexible quality.

' The relative proportions of lime cooked and caustic cooked straw will vary in accordance with the condition of the straw, that is, as to whether the straw is clean and bright, or whether it is partially decomposed. Good clean dry straw unrotted, is preferable. The sheet produced is somewhat darker than that made from lime cooked straw alone.

The mixing-"or" lime cooked straw with caustic cooked straw in the manner above described, enables the paper machines to run at approximately the same speed, as with regular lime cooked straw, and "at a higher speed than with straight caustic cooked straw. On the 'corrugators, the mixed caustic and lime cooked straw will run at a higher speed than the straight lime cooked straw. In addition, there. is less trouble in combining the composite board when the mixed pulp is used. Straight caustic cooked straw forms a sheet of such texture that silicate does not readily cause it to adhere to the liner arranged on either side, so that some trouble results in the sticking of the board.

The mixed pulp is free from this trouble. Considerable variation may be made in the proportions of the constituents of the mixture, as for instance, instead of a half and half mixture, three parts of either may-beused with two parts of the other, the proporin providing a pulp for the formation of the 1 board, composed of substantially equal portions of separately cooked lime and caustic soda pulp.

3. The step in the method of producingstraw board for corrugating, which consists in digesting or cooking separate batches of straw with lime and caustic soda respectively, each for about sevenhours, under about twenty-five pounds steam pressure.

4. The method of producing straw board for corrugating, which consists in digesting or cooking separate batches of straw with lime and with caustic soda respectively, mixing the batches after cooking, and forming the mixed pulp into paper.

5. The method of producing straw board for corrugating, which consists in digesting" or cooking separate batches of straw with lime and with caustic soda respectively, mixing the batches after cooking, washing, and forming the pulp into a sheet or web.

6. The method of producing pulp for corrugated straw board, which consists in d1- gesting or cooking separate batches of straw with lime and caustic soda respectively, each for about seven hours, under about twentyfive pounds steam pressure, cutting ed the steam and rolling for about two hours.

7. A straw board for corrugatin com posed of mixed batches of straw pu p, se arately digested by lime and caustic soda respectively.

8. A corrugated straw board for the inner layer of composite packing boards, composed of substantiall equal parts of separately cooked lime an caustic soda pulps.

9. A straw board for corru ating som posed of mixed pulps digested y lime and caustic soda respectively.

10. A straw board for corrugating, composed of a mixture of separately digested long and short fiber.

Signed at Terre Haute, in the county oi Vigo, and State of Indiana, this *lth day of Feb, A. l). 1929.

EDWARD B. WESTGN. WILLIAM G. CLARK. 

